Prior art solid state image detectors include a photosensitive diode which is reverse biased to generate a current creating a voltage drop across a resistive load such as a metal oxide semiconductor field effect transistor (MOSFET) in response to radiation incident upon the detector. A disadvantage is that when such a detector and resistive load device are used to control charge injection to a charge coupled device in a focal plane array, the MOSFET serving as the load device for the photodiode takes up a significant amount of space on the semiconductive substrate supporting the detector and the charge coupled device, thus limiting the device density on the substrate.
One problem in focal plane array imagers is that a scene to be viewed by the imager contains both radiation defining the image to be viewed and background radiation which contains no desirable information. If the background radiation is of sufficient intensity, the imager may be saturated, requiring adjustments to the imager which severely limits its dynamic range. In order to avoid this difficulty, the prior art required that an additional device, namely a coupling capacitor, be formed on the semiconductive substrate, to filter out the constant background signal, further limiting the available space on the substrate and decreasing the device density.